1. Field of the Invention
The present invention relates generally to novel flame-retarded, flexible polyurethane foams.
2. Description of the Prior Art
The flexible polyurethane foams that are a part of the invention are well known in the industry. Information on preparation and common reactants can be found in many resources, including the Encyclopedia of Polymer Science and Engineering, Vol. 13, copyright 1988, John Wiley & Sons, Inc.
Polyurethane foam is formed by a reaction between a polyol and diisocyanate. This reaction is highly exothermic. A complicating factor in the preparation of polyurethane foams is that certain of the foam forming reactions are reversible at high temperature.
Recently there has been an industry trend to move to lower density polyurethane foam. One result of this trend is that as the density of the foam decreases, the exotherm generated during the preparation of the foam increases, due to the high concentration of water needed to lower the density. Specifically it is the reaction of TDI and water that generates the largest exotherm during the polyurethane reaction.
One method that has been used to reduce this large exotherm is to use an auxiliary-blowing agent such as freon or methylene chloride. The addition of the auxiliary blowing agent reduces the amount of water needed to achieve the desired density and due to the lower amount of water, the exotherm is reduced.
Many auxiliary blowing agents that have been used in the past such as freons, hydrofluorcarbons and methylene chloride have come under attack recently for environmental reasons. The foam industry has since sought to prepare low density foams without the use of auxiliary blowing agents.
Forced air-cooling described in U.S. Pat. No. 5,171,756 incorporated herein by reference is one method that has been used by the foam industry to avoid the damage caused by the high exotherms of the polyurethane reaction. The method involves drawing cool air through the foam block.
Forced air cooling of polyurethane foam also has its own drawbacks of poor cure and loss of strength and integrity on the side of the bun that is closest to the exit for the airflow. One way the industry has tried to avoid this problem has been to wait a period of time before performing the forced air-cooling. However this allows a build up of heat due to the exotherm, which can also cause poor cure and loss of strength and integrity to the foam.
The use of flame retardants in polyurethane foam is well known. It has been observed that flame retarded foam is more sensitive to the waiting period required by forced air cooling and experiences a higher degree of poor cure and loss of strength and integrity than non-flame retarded foam.
One method of reducing the poor cure and loss of strength and integrity in flame retarded foam has been to use a flame retardant mixture based on brominated diphenylethers (optionally in combination with triaryl phosphates) mixed with an acid scavenger. The addition of the acid scavenger to the flame retardant mixture reduces the amount of poor cure and loss of strength and integrity caused by the forced air cooling.
The brominated diphenylether based flame retardants have come under attack recently for suspected environmental concerns. The foam industry has since sought to prepare foams without the use of brominated diphenylether based flame retardants.
What is needed is a means of preventing the poor cure and loss of strength and integrity of the flame retarded forced air-cooled foams without brominated diphenylether based flame retardants. The present invention addresses this need.